Twin roller casting

ABSTRACT

A twin roll casting machine has an end-dam structure at each end of the pair of rolls. Each end-dam structure comprises a first part which is urged into engagement with the rolls in the vicinity of the narrowest part of the gap with a contact pressure which prevents leakage of molten metal. A second part, positioned above the first part, is urged into engagement with the rolls with a contact pressure which is less than that of the first part, but which nevertheless prevents leakage of molten metal.

This invention relates to a twin-roll continuous casting machine inwhich a pool of molten metal is contained between a pair of spaced apartrotatable rolls and a pair of end dams urged against the ends of therolls and on rotating the rolls, solidified shells of metal formed onthe roll surfaces are continuously passed through the narrowest part ofthe gap between the rolls and are bonded together to form strip.

Each end dam is subjected to forces tending to push the end dam awayfrom the ends of the rolls and external pressure has to be applied tothe end dam to prevent this from occurring. The forces applied to theend dam which tend to push the end dam away from the rolls are due to

(a) hydrostatic pressure of the molten metal,

(b) motion of the molten metal in the pool, and

(c) sideways spreading of the metal as it undergoes hot deformation asit passes through the narrowest part of the roll gap.

The force (c) is by far the greatest and most variable of the threeforces and so the end dam has to be urged against the ends of the rollswith a force which is greater than this force (c) so that leakage doesnot occur. It will be appreciated that there is wear between thestationary end dam and the ends of the rotating rolls and the greaterthe contact pressure between the end dam and the rolls, the greater thewear.

Furthermore, the upper part of the end dam which helps to locate themolten pool should not encourage solidification of the molten metalwhereas the lower part of the end dam does not necessarily have topromote solidification although it may be beneficial.

An object of the present invention is to provide a twin-roll continuouscasting machine having improved end-dams.

It is known from JP-A-60 148646 for a twin roll continuous castingmachine to have a pair of end dam structures disposed at and urged intoengagement with the axial ends of a pair of rotatable rolls. Each enddam structure comprises three parts arranged in a stack. The uppermostdam part presses against the ends of the rolls with a constant pressureand each of the lower two parts are urged against the ends of the rollssuch that if the pressure applied to these parts by the solidifiedcasting exceeds a predetermined value, the parts move away from the endsof the rolls and return into engagement with the ends of the rolls whenthe pressure is reduced below the predetermined value.

According to the present invention a twin-roll continuous castingmachine comprises a pair of rotatable rolls arranged in side-by-sideparallel relation with a gap therebetween and a pair of end damstructures disposed at and urged into engagement with the axial ends ofthe roll barrels so that in use, a pool of molten metal is containedbetween the rolls and the end dam structures and solidified shells ofmetal pass continuously through the narrowest part of the gap betweenthe rolls and are bonded together to form strip; characterised in thateach end dam structure comprises a first part located adjacent thenarrowest part of the gap and a second part above the first part, saidfirst part being mounted on a support arm which has means for urging thesupport arm towards the ends of the roll barrels to force the first partinto engagement with the ends of the roll barrels and pressure exertingmeans mounted on the support arm which serve to urge the second partinto engagement with the ends of the roll barrels, said first part beingurged into engagement with the rolls with a contact pressure which maybe different than that between the second part and the rolls.

The part of each end dam which abuts the rolls adjacent the narrowestpart of the gap is subjected to force (c) referred to above and thepressure applied by the support arm to this part of the end dam issufficiently large to maintain sealing with the ends of the rolls.

The other part of the end-dam is usually subjected to a lower contactpressure with the ends of the rolls because the pressure exerted by themolten metal on this part of the end dam is lower.

By splitting the loadings on the end dam, if the load on the lower partis exceeded, the seal between the upper part of the end dam is likely tobe maintained due to the independent loading. The possibility ofrecovering the situation and having the seal restored between the lowerpart of the end dam and the rolls is increased when there is differentloadings on the two parts of the end dam. If the two parts of the enddam are of different materials it is likely that there will be adifference in wear of the materials. Having each part loadedindependently compensates for the differential wear thus maintaining theseal.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more readily understood it will nowbe described, by way of example only, with reference to the accompanyingdrawings in which

FIG. 1 is a diagrammatic side view of one end of a twin roll caster,

FIG. 2 is a sectional side view of an end dam structure in accordancewith the present invention and

FIG. 3 is an end view of the structure shown on section line III--III ofFIG. 2.

A twin-roll continuous caster comprises a pair of rotatable rolls, oneof which is indicated in FIG. 1 by reference numeral 1, arranged withtheir axes of rotation substantially horizontal and positioned inside-by-side relation with a gap between the rolls. Each roll has a stubshaft at each end of its roll barrel and the rolls are rotatably mountedwith the stub shafts in support housings (not shown) and means (also notshown) are employed to rotate the rolls. At each end of the pair ofrolls an end dam structure 3 is provided which bears against the ends ofthe roll barrels with sufficient contact pressure to enable a pool ofmolten metal to be contained between the rolls and the end dams withoutsignificant leakage between them. The surface of the molten pool isindicated by reference numeral 5 in FIG. 1. In use, the rolls are cooledand are rotated so that the roll surfaces in the gap between the rollsare moving downwardly. Shells of solidified metal are formed on eachroll where the pool contacts the cooled roll surface and as the rollsare rotated the shells come together at the narrowest part of the gapbetween the rolls and are bonded together by the pressure exerted by therolls to form a metal strip.

As shown in FIG. 1, the end dam structure 3 comprises a first part 7which is adjacent the narrowest part of the roll gap and a separateindependently movable second part 9 above the first part. A support arm11 is pivoted at its lower end and the part 7 is secured to the supportarm. Means not shown, but which usually comprises one or more fluidoperated rams, exerts a pressure P on the support arm to pivot the armand force the part 7 of the end dam against the ends of the roll barrelswith sufficient force to prevent leakage between the part 7 of the enddam and the ends of the rolls. This force has to overcome at least theforce which is exerted on the end dam by the solidified metal as itpasses through the narrowest part of the roll gap. The part 9 of the enddam also has to be urged against the ends of the roll barrels to preventleakage but usually a lower pressure is required than that required bypart 7 and so a plurality of pressure exerting means 13 are mounted onthe support arm 11 and act between the support arm and the part 9 of theend dam. The pressure exerted on the part 9 by the means 13 is such asto result in a contact pressure which prevents leakage between the part9 and the ends of the roll barrels but it is usually less than thecontact pressure between the part 7 and the rolls barrels.

The part 7 is of a material which has low wear properties because thehigh contact pressure between the part and the ends of the roll barrelscould lead to rapid wear of the material. It may be a refractorymaterial, and therefore can have suitable thermal insulating properties,or a metal such as copper which is cooled.

The part 9 is subjected to a lower contact pressure with the ends of theroll barrels and so it is not so prone to wear and can have higher wearproperties than the material of part 7. The part 9 should not encouragesolidification of the molten metal in the pool on this part of the enddam.

Referring now to FIGS. 2 and 3, the first part 7 of the end damstructure comprises a body of refractory material 15, such as sialon orboron nitride based material, mounted on a cooled metal plate 17. Theplate is pivotally mounted on a bracket 19 projecting from a support arm21. The second part 9 of the end dam comprises a refractory plate 23such as fused silica which is mounted in face-to-face relation with thefront face of a metal plate 29. Preheating is used to heat therefractory plate 23 prior to introducing molten metal into contacttherewith to discourage metal in the pool from solidifying in contactwith the plate. This may be brought about by electrical heaters 25located in slots 27 in the refractory plate 23. On the back of the metalplate 29 there are three self aligning couplings 31 to which fluidoperable rams 33 are connected. These rams are mounted on the supportplate 21 and so the pressure between the support plate and the secondpart of the end dam can be adjusted.

The support plate is pivoted at its lower end and is urged towards theends of the roll barrels by one or more rams (not shown) to cause thebody 15 to engage the ends of the roll barrels with a sufficiently highcontact pressure to prevent leakage of molten metal. The provision ofthe rams 33 permit the upper plate 23 to be urged against the ends ofthe roll barrels with a lower contact pressure than the contact pressurebetween the body 15 and the rolls but still prevent leakage of moltenmetal.

The rams 33 shown in FIG. 2 are conveniently pneumatic cylinders with aspring return but any form of pressure exerting means may be employed.Any convenient number of pressure exerting means may be employed.

Each end-dam structure may be vibrated in the direction parallel to thedepth of the gap between the rolls, i.e. when the roll axes are paralleland in a horizontal plane, the end dams are vibrated vertically.

We claim:
 1. A twin-roll continuous casting machine comprising:a pair ofparallel, side-by-side rotatable roll barrels (1) with a gaptherebetween; a pair of end dam structures (3) disposed at and urgedinto engagement with axial ends of the roll barrels, wherein a pool (5)of molten metal is contained between the roll barrels and the end damstructures, wherein solidified shells of metal pass continuously throughthe narrowest part of the gap between the roll barrels and wherein thesolidified shells of metal are bonded together to form a strip; whereineach end dam structure comprises:a first part (7, 15) located adjacentthe narrowest part of the gap, a second part (9, 23) located above thefirst part, a support arm (11, 21) wherein said first part is mounted onsaid support arm and said second part is coupled to said support arm,and a single means for urging the support arm towards the ends of theroll barrels to force the first part (7, 15) into engagement with theends of the roll barrels; and at least one pressure exerting means (13,33) mounted on the support arm which urges the second part (9, 23) intoengagement with the ends of the roll barrels, wherein the first part (7,15) and the second part (9, 23) are urged by the support arm atdiffering pressures.
 2. A twin-roll continuous casting machine asclaimed in claim 1 in which the pressure exerting means is so arrangedthat the first part (7, 15) is urged into engagement with the rollbarrels with a higher contact pressure than that between the second partand the roll barrels.
 3. A twin-roll continuous casting machine asclaimed in claim 1 in which the first part (15) has lower wearproperties than the second part (23).
 4. A twin-roll continuous castingmachine as claimed in claim 1 in which the first (15) and second (23)parts are made of different refractory materials.
 5. A twin-rollcontinuous casting machine as claimed in claim 1 in which the secondpart (23) has thermal insulating properties in order to retardsolidification.
 6. A twin-roll continuous casting machine as claimed inclaim 1 in which the second part (23) has provision (25) for heatingthat part which is to be adjacent the molten metal prior to introducingmolten metal into contact with the part.
 7. A twin-roll continuouscasting machine as claimed in claim 1 in which the first part (15) hasprovision for cooling the part to promote solidification of the materialin the gap.
 8. A twin-roll continuous casting machine as claimed inclaim 1 in which the pressure exerting means (33) comprise one or morefluid-operable means.
 9. A twin-roll continuous casting machine asclaimed in claim 1 in which means are provided for vibrating eachend-dam structure in the direction parallel to the depth of the gapbetween the rolls.
 10. A twin-roll continuous casting machinecomprising:a pair of spaced rotatable rolls arranged in a side by sideparallel relation and having a gap therebetween; a pair of end damstructures disposed at and urged into engagement with respective axialends of said pair of rotatable rolls wherein, in use, a pool of moltenmetal is contained between said pair of rotatable rolls and the end damstructures and wherein solidified shells of metal pass continuouslythrough a narrowest part of the gap between the rolls, the solidifiedshells of metal being bonded together to form a strip; each said end damstructure comprising:a support arm, said support arm being pivotablymounted on an adjacent support surface, a first part rigidly mounted tosaid support arm, a second part located above said first part, saidsecond part being resiliently mounted to said support arm; and a meansfor exerting pressure on said support arm for urging the support armtowards the end faces of the pair of rotatable rolls, wherein said firstpart is urged into engagement with the rolls with a contact pressurewhich is greater than a contact pressure of said second part against therolls.
 11. The twin roll continuous casting machine of claim 10 whereinsaid first part is made of a material which has lower wear propertiesthan a material from which said second part is made.
 12. The twin rollcontinuous casting machine of claim 11 in which said first and secondparts are made of different refractory materials.
 13. The twin rollcontinuous casting machine of claim 10 in which said second part is madeof a material that has thermal insulating properties in order to retardsolidification.
 14. The twin roll continuous casting machine of claim 10further comprising a means for heating said second part prior tointroducing molten metal into contact with the part.
 15. The twin rollcontinuous casting machine of claim 10 further comprising a means forcooling said first part to promote solidification of the material in thegap.
 16. The twin roll continuous casting machine of claim 10 furthercomprising at least one fluid operable pressure exerting meanscontacting said second part for urging said second part toward said endfaces of said pair of rotatable rolls.
 17. The twin roll continuouscasting machine of claim 10 further comprising at least one spring,mounted between said support arm and said second part, for urging saidsecond part toward said end faces of said pair of rotatable rolls. 18.The twin roll continuous casting machine of claim 10 further comprisinga means for vibrating each end dam structure in a direction parallel toa depth of the gap between said pair of rolls.